When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). This may be aggravated in internal combustion engine applications through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber of the engine when the temperature is high during or after the combustion event.
Conventional NOx reduction techniques may be implemented, such as including a NOx emissions filter in-line with the exhaust stream. With such techniques, it is typically useful to determine the NOx content of the exhaust gas exiting the engine.
The NOx content of the exhaust gas produced by the engine is may be or otherwise determined directly with a conventional NOx sensor. NOx sensors are well known in the art and commercially available. In typical applications, the NOx sensor is exposed to the exhaust gas to produce a signal indicative of the NOx content of the exhaust gas. However, after prolonged exposure to the exahust gas, NOx sensors have been known to degrade thereby affecting the long-term durability and reliability of the NOx sensor and, accordingly, the accuracy of the NOx content measurement.